Separation of diethylbenzene



Nov. 10,1970 ,R. P. BROWN ETAL I 3,539,623

SEPARATION OF DIETHYLBENZENE Filed April 18, 1966 3 Sheets-Sheet l OXIDIZE (VERY MILD) 60-.

a DISTILL META ETHYLACETO- PHENONE PRODUCT v {24 OXIDIZE (MODERATE) 35 DISTILL A CRYSTALLIZE META D|ACETYL V BENZENE PRODUCT OXIDIZE cs'rnons) v 22 5 FILTER ISOPHTHALIC ACID PRODUCT L I8 'ro STORAGE fi-suasnmmux PURE META DIETHYLBENZENE OVERHEAD 10 SEPARATION BY FRACTIONAL MIXED DIETHYL- BENZENE ISONERS 16 1 WSUBSTANT'IALLY PURE PARA a ORTHO DIETHYLBENZENE BOTTOMS MIXTURE r34 DEHYDROGENATION a DISTILLATION 44 OXIDIZE cs-raoum 46 .36 FILTER s-LEAcH TEREPHTHAUC ACID PRODUCT r38 48 I OXIDIZE CMODERATE) r50 & CRYSTALLlZE BENZENE PRDOUCT 52 1 PARAOIVINYLBENZENE PRODUCT ox|o|zE (VERY r54 PARA-ETHYLACETO- PHENONE PRODUCT- I42 HYOROGENATION 8 'DISTILLATION PARA-DIETHYLBENZENE Papouc-r INVENTORS RENE P. BROWN E BIRT ALLISON, JR.

PIERRE MARIE JOSEPH GHISLAIN DE RADZIT'ZKY D'OSTROWICK M mic/M.

United States Patent Texas Filed Apr. 18, 1966, Ser. No. 543,377 Int. Cl. C07c 51/20, 7/00 US. Cl. 260--524 8 Claims ABSTRACT OF THE DISCLOSURE Superdistilling an isomeric mixture of diethylbenzenes to obtain overhead relatively pure metadiethylbenzene and a mixture of paraand otho-diethylbenzene as bottoms. Chemically converting the bottoms and separating the isomeric products formed.

This invention relates to resolution of a mixture of diethylbenzene isomers; to separation of relatively pure rnetadiethylbenzene as a distillation overhead fraction from a relatively pure paraand ortho-diethylbenzene bottoms mixture; to the processing of diethylbenzene hydrocarbon fractions by oxidation or dehydrogenation of at least one alpha-ethyl carbon atom into more readily resolvable isomeric components; to production of oxidation products thereof, namely isophthalic acid, terephthalic acid, para-ethyl-acetophenone, para-diacetyl-benzene; to unchanged pure or relatively concentrated metadiethylbenzene; to concentrates of orthoand para-diethylbenzenes to low in meta-isomer content; and to the intermediate relatively pure isomeric products formed thereby.

Meta-diethylbenzene is reported to have about a 2 C. boiling point margin above its orthoand para-diethylbenzene isomers, the latter two isomers boiling less than 0.5 C. from each other. Consequently, the resolution of a mixture of diethylbenzene isomers by distillation would not have appeared to be possible. Nevertheless, it has been found, according to one aspect of this invention, that better than 93% pure, usually better than 95% pure, and, for some fractions, better than 98% pure metadiethylbenzene can be separated overhead from its mixture with the orthoand para-diethylbenzene isomers by distillation. That order of purity identifies the separated meta-diethylbenzene product as sufficiently pure for practical further processing to other valuable products derivable from meta-diethylbenzene and now made available by this invention most economically and in an adequately pure state.

In a further aspect of this invention, the separation of the meta-diethylbenzene by simple distillation from the mixture leaves a bottoms intermediate mixture of paraand ortho-diethylbenzene isomers which, while inseparable by distillation, are nevertheless sufficiently pure by having such reduced content of meta-diethylbenzene,

such as usually less than that this bottoms product may now be practically chemically treated either by oxidation or dehydrogenation of one or both alpha-ethylcarbon atoms, whereby a mixture of para-divinylbenzene, para-ethylvinylbenzene and ortho-ethylvinylbenzene is formed by the dehydrogenation and such products as r 4 3,539,623 Patented Nov. 10, 197

readily separable terephthalic acid, para-diacetyl benzene, isophthalic acid, para-ethyl-acetophenone, meta-ethylacetophenone and the like are formed by the oxidation. In the direct dehydrogenation of the bottoms mixture comprising paraand ortho-diethylbenzene, any orthodivinylbenzene formed cyclizes to easily separable naphthalene.

According to this invention we have found that a mixture of ortho, metaand para-diethylbenzene isomers are efficiently processed to separate or reform the isomers into usefully pure products. The initial isomeric mixture preferably contains a substantial proportion, such as at least 20%, and usually a quantity in the range of 20 to of meta-diethylbenzene, based on the weight of the mixture. Meta-diethylbenzene can be separated from such mixture as a substantially pure distillation overhead; that is, better than 93% pure, preferably at least 95% and, if desired, 98 to 99% pure. In such distillation we use a column still of at least 100 trays, preferably at least 200 trays at a reflux ratio of at least 30:1, usually about 40:1. A meta-diethylbenzene isomer of such degree of purity was never heretofore practically obtained by distillation. It may be directly processed to various derivatives such as by oxidation or dehydrogenation, sulfonation, halogenation and the like.

A preferred procedure is to oxidize the meta-isomer to meta-ethyLacetophenone, diacetyl benzene and isophthalic acid, products available as desired by application of progressively severe oxidations which heretofore were exceedingly difiicult to obtain in a correspondingly pure form. The bottoms mixture, too, is then oxidized progressively to form such alternate oxidation products.

In another alternate procedure, the mixed bottoms isomers are dehydrogenated to a mixture of para-divinylbenzene, para-ethylvinylbenzene and ortho-ethylvinylbenzene. The para-divinyl compound can be separated as a distillation concentrate which can be hydrogenated selectively under controlled conditions to convert the divinyl-benzene and ethylvinyl-benzene to a para-diethylbenzene rich product from which is recovered pure paradiethylbenzene such as by further distillation.

As an alternate procedure the dehydrogenated mixture of para-divinylbenzene and ethylvinyl-benzenes may be purified by crystallizing the same which are readily resolvable by distillation and crystallization, any orthodivinvylbenzene being cyclized to naphthalene in the dehydrogenation.

A practical source of the mixed ortho, metaand para-diethylbenzene isomer starting material has been as a by-product of production of ethylbenzene. In the catalytic alkylation of benzene with ethylene or ethyl chloride to produce ethylbenzene, some diethylbenzene mixed isomers are also formed. The diethylbenzene mixture may accumulate as bottoms in the ethylbenzene distillation. Moreover, some ethylbenzene may contaminate the bottoms. Other impurity may occur in the alkylate such as some C hydrocarbon, such as theyl toluenes and propylbenzene, and these may also contaminate the diethylbenzene bottoms. These impurities amount, after substantial accumulation with the bottoms, to from 0.1 to about 5% of the bottoms, depending upon the extent that they had been allowed to accumulate with the diethylbenzene bottoms.

It is possible, however, in the ethylbenzene distillation to remove the residual ethylbenzene as well as the C hydrocarbon as an intermediate side stream in the ethylenzene distillation so that only a relatively pure isomeric mixture of diethylbenzenes accumulates as bottoms during the main distillation of ethylbenzene. However, it is preferred to preliminarily purify the feedstream as shown in FIG. 2 and further described below.

The invention is further explained in conjunction with the drawings wherein:

FIG. 1 is a process chart illustrating generally the course of processing and the various alternatives that may be followed, all in accordance with the present invention;

FIG. 2 is a flow diagram of a continuous process for the separation of diethylbenzene into a meta-rich fraction and a paraortho-rich fraction, and including subsequent process steps which may be conducted to produce a variety of products;

FIG. 3 illustrates two alternate oxidation processes which may be conducted on the para-, orthodiethylbenzene concentrate to obtain ultimate products of high purity; and

FIG. 4 illustrates two alternate oxidation processes Which may be conducted on the meta-isomer to obtain ultimate products of high purity.

Referring to FIG. 1, a purified mixture of diethylbenzene isomers enters the system through line 10 in a distillation zone 12 to separate relatively pure meta-diethylbenzene overhead by way of line 14 and a bottoms mixture comprising substantially ortho and paradiethylbenzones with a small quantity of less than and usually less than 2% of residual meta-diethylbenzene in line 16.

In alternate processing the overhead substantially pure meta-diethylbenzene may be sent to storage by way of line 18 for use as such. It is preferred to oxidize overhead pure meta-diethylbenzene in either of three alternate procedures:

A first alternate procedure is to heavily oxidize the meta-diethylbenzene to iso-phthalic acid in an oxidation zone 20. The iso-phthalic product, after purification and recovery, is sent to storage by way of line 22.

In a second alternate oxidation, the meta-diethylbenzene from line 14 is sent to a milder oxidation zone 24 where the product is oxidized to meta-diacetylbenzene where the product, after purification, is sent to storage by way of line 26.

In a third alternate oxidation procedure the meta-diethylbenzene may be subjected to oxidation under very mild conditions to produce meta-ethylacetophenone in oxidation zone 28. It is then purified and sent to storage by way of line 30.

The bottoms product of the initial distillation from still 12 in line 16 may also be treated in alternate procedures:

In a first alternate procedure, the mixture in line 32 is sent to a dehydrogenation zone 34 to produce a dehydrogenation mixture of para-divinylbenzene, para-ethylvinylbenzene and orthoethylvinylbenzene. In that treatment most of the orthoproduct entering the dehydrogenator is converted to naphthalene. In further treatment the dehydrogenation product in line 36 may be resolved by crystallization, separating the divinylbenzene from the mono-vinyls thereby in a zone 38.

Alternately, the dehydrogenation product may be passed through line 40 and hydrogenated in a zone 42 to produce a product which is largely para-diethylbenzene and which may be separated from the minor residual ortho and naphthalene impurity content by distillation.

In a further alternate procedure, the bottoms product passing through line 16 may be subjected to oxidation. A drastic oxidation preformed in zone 44 converts the para-diethylbenzene to terephthalic acid which is readily purified and sent to storage by way of line 46.

In a milder oxidation the bottoms mixture in line 16 may be converted largely to para-diacetylbenzene in zone 48, and after purification, is withdrawn through line 50 to storage.

In a most mild oxidation, the product mixture in line 16 may be oxidized in zone 52 to para-ethylacetophenone which, after purification, is withdrawn to storage through line 54.

The operation of the process is further explained in the following as typical examples:

EXAMPLE 1 Referring to FIG. 2, a polyalkylbenzene stream 11 recovered as a by-product from an alkylation plant in which ethylbenzene is produced by alkylation of benzene with ethylene is fed to a fractionating train 13. The fractionating train consists of column 15, which has approximately theoretical separation stages, and column 17, which has approximately 10 theoretical separation stages. The overhead product stream 9 from column 15 consists of light impurities which may be recycled to the alkylation plant or otherwise disposed of. Bottoms stream 19 from column 15 is fed to column 17, which separates the feed into a bottoms stream 21 and an overhead stream 23. Bottoms stream 21, which consists of heavy components, primarily polyalkylbenzenes, is recycled to the alkylation plant. The overhead stream 23 contains the desired mixed diethylbenzenes for further processing in accordance with the present invention.

Stream 23 is fed to the superfractionator, designated generally by the numeral 25. The superfractionator consists of fractionating columns 27 and 29, which are arranged in series. In place of columns 27 and 29, one large column could be used, but the division in two columns, with series hookup, is used in order to reduce the physical size of the superfractionator. Each of columns 27 and 29 provide approximately theoretical separation stages for each column. In view of the series hookup, note that vapor is conveyed from the top of column 27 into the bottom of column 29 via line 31, and that liquid is conveyed from the bottom of colmn 29 to the top of column 27 via line 33. A reflux condenser 35 is provided to receive the overhead vapor 37 conveyed from the top of column 29. A reflux line, running from the reflux condenser 35 back into column 29, carries a reflux stream in quantity of approximately 40 by weight, of the overhead stream 37. A bottoms stream 41 exits from the bottom of column 27. An analysis of the more significant streams, just discussed, is given herebelow in Table 1.

TABLE I Stream line number Analysis, weight percent Ethylbenzene 0. 3 9. 4 Cumene 0.3 9. 4 Bntyl benzenes 2. 6 75. 3 0. 2 0.2 Meta-diethylbenzene 5. 3 5. 5 56. 9 1. 0 62. 5 98. O 2. 1 Para-diethylbenzen 5. 4 0. 3 26. 2 O. 5 28. 4 1. 0 74. J Ortho-diethylbenzene 7. 9 0. 1 8. 2 0. 2 8. 9 0. 6 23. O Triethylbenzene and heavier 8. 2 8. 5 98. 3 0. 4

1 Trace.

From the foregoing table, attention is directed to the high purity of the meta product obtained from the top of column 29, i.e., 98%. Moreover, attention is directed to the low meta content of the bottoms stream 41 from column 27 of the superfractionator 25. Thus, the bottoms product from the superfractionator contains only 2.1% meta, the major part of the bottoms material consisting of about three-fourths para-diethylbenzene and one-fourth orthodiethylbenzene.

Based on the stream 23 fed to the superfractionator, a yield of 63% by weight is obtained from the overhead stream 37, a yield of 37 weight percent is obtained from the bottoms stream 41.

After separation of the diethylbenzenes into a substantially pure meta-diethylbenzene overhead and a substantially pure paraand ortho-diethylbenzene bottoms mixture, subsequent processing is made possible. The examples which follow are indicative of that processing. It should be noted that in certain instances in the examples the feed streams will not correspond precisely in composition to the meta-overhead stream 37 and the para-, orthobottoms stream 41 in the specific operation in accordance with EX- ample I; however it will be appreciated that slightly varied conditions vary the composition of the metastream, and orthoand parastream. Thus, reflux ratio may either be increased or decreased; the operation of the distillation train supplying raw feed to the superfractionator may be varied somewhat; the composition of the input stream to the fractionation train 13 (FIG. 2) may be changed somewhat; the column conditions for the superfractionator 25 may be varied somewhat; and the point of introduction of the feed 23 to the superfractionator may be varied. Accordingly, it will be appreciated that the following examples are indicative of operation with overhead and bottoms product from a superfractionator operating generally in accordance with Example I and on a feed comparable thereto.

EXAMPLE II A feed of a composition similar to that of bottoms product 41 of Example I is utilized as a feed to an oxidation process for making terephthalic acid. The method used for this oxidation is further described in U.S. Pat. No. 2,766,281 for the nitric acid oxidation of xylenes. As suggested in this patent, chlorinated diphenyl (48% chlorine) is used as dispersing agent so that efficient stirring is possible throughout the reaction. 50 grams of a diethylbenzene mixture (ortho 21%, para 76%) is mixed with 50 grams of chlorinated diphenyl (48% chlorine). The diethylbenzene solution is heated to 125 C. and then 70% aqueous nitric acid (d. 1.42) is added dropwise at a mean rate of 1.15 ml. per minute; after the addition of 30 ml. of 70% HNO the temperature is raised to 180C. Water added with HNO and produced during the reaction is removed continuously from the reaction vessel and is collected in a condenser. A total of 390 ml. of nitric acid is added in 340 minutes.

After cooling at room temperature the reaction mixture is mixed with ether and 28.6 grams of a pale yellow product was separated by filtration. This product is then extracted with hot water and acetone in order to leach out phthalic acid and acetylbenzoic acid. One obtains a yield of 74.5 weight percent of terephthalic acid on contained para-diethylbenzene or a 60.15 molar yield.

EXAMPLE III A product similar to the bottoms product 41 obtained from the column 27 of fractionating train 25, Example I, has the following analysis:

Component: Wt. percent Meta-diethylbenzene 4.3 Para-diethylbenzene 74.3 Ortho-diethylbenzene 21.4

The above-identified stream is charged to a fixed-bed dehydrogenation reactor, together with steam mixed therewith in a steam-hydrocarbon mole ratio of approximately 50:1. The steam-hydrocarbon mole feed mixture is fed continuously to the reactor at a temperature of approximately 600 'C. The effluent from the reactor is condensed to form separate layers of water and hydrocarbon. An analysis of the hydrocarbon layer from the reactor efiluent is as follows:

Component: Wt. percent Benzene 0.8

Toluene 0.7 Ethylbenzene 0.4

In addition to the above liquid product, a non-condensable gas fraction is produced in the reactor. It is a mixture of hydrogen, methane, and other light gases. The yield of the liquid hydrocarbon, from the efiluent, is approximately by weight, based on the hydrocarbon charge. The liquid hydrocarbon obtained from the eflluent is subjected to distillation at a pressure of approximately 50 mm. absolute in a column providing 70 theoretical separation stages, and at a reflux ratio of about 20:1. The bottoms product has the following analysis:

Component: Wt. percent p-Diethylbenzene 0.4 Meta-ethylvinylbenzene trace Para-ethylvinylbenzene 46.4 Ortho-ethylvinylbenzene 3.3 Meta-divinylbenzene 1.6 Para-divinylbenzene 42.3 Naphthalene and heavier 6.0

The bottoms product just identified is then subjected to hydrogenation in a hydrogenation reactor using a cobaltmolybdenum catalyst under the following conditions:

Catalyst: Cobalt/molybdenum Volume feed/volume catalyst/hour 0.5/1 H /H.C. Ratio (molar) 5/1 Temperature F 650 Pressure p.s.i.g 300 The efliuent from the hydrogenation reactor is cond'ensed and the hydrogen separated therefrom. The remaining liquid is found to have the following analysis:

Component: Wt. percent Para-diethylbenzene 88.9 Meta-diethylbenzene 1 .5 Ortho-diethylbenzene 3.1 Benzene 0.4 Ethylbenzene 0.6 Naphthalene and heavy material 3.6 Heavy fraction 1.9

Such liquid is then subjected to distillation to yield a light fraction consisting primarily of benzene and ethylbenzene, a heavy fraction, and a middle cut consisting of the following:

Component: Wt. percent Benzene and ethylbenzene trace Para-diethylbenzene 95.0 Meta-diethylbenzene 1.7 Ortho-diethylbenzene 3.3 Heavy components trace It is seen that the resulting middle cut is a para-diethylbenzene product of rather high purity.

EXAMPLE IV As an alternate procedure to the one described in Example III preceding, the bottoms product obtained on distilling the liquid hydrocarbon at a pressure of 50 mm. absolute, using approximately 70 theoretical separation stages and at a reflux ratio of about 20: 1, is fed to a distillation column wherein a heavy fraction, primarily naphthalene and heavier, is removed. A light fraction is obtained as follows:

Component: Wt. percent Diethylbenzene 0.4 Meta-ethylvinylbenzene trace Para-ethylvinylbenzene 49.4 Ortho-ethylvinylbenzene 3.5 Meta-divinylbenzene 1.7 Para-divinylbenzene 45.0

This light fraction is subjected in a two-step crystallization process to yield a para-divinylbenzene solid product and a mother liquor of the composition indicated hereinafter:

1 Trace.

The yields of mother liquor and para-divinylbenzene product as identified above were, respectively, 57.8% and 42.2% by weight, based on the light fraction which was used as the feed to the crystallization.

EXAMPLE V 86.5 grams (100 ml.) of high purity meta-diethylbenzene of the composition of stream 37 from column 29 from the superfractionator 25 of Example I is mixed with 100 grams of chlorinated diphenyl (487 chlorine) and treated as in Example II. A total of 960 ml. of 70% nitric acid are added in 660 minutes. The reaction product is then filtered at about 100 C. and then washed at room temperature with acetone. The solid product contains 91% isophthalic acid. One obtains a yield of 69.4 weight of isophthalic acid based on meta-diethylbenzene or a 56% molar yield. It must be understood that nitric acid oxidation is not the only method for transforming diethylbenzenes into phthalic acids; therefore, Examples II and V are not examples of a preferred method and are only given as an illustration of how this transformation can be carried out by known methods.

EXAMPLE VI A feed material is utilized having a composition similar to that of the bottoms stream 41 of column 27 of the super fractionator 25, the analysis of the feed material being as follows:

Components: Wt. percent Ortho-diethylbenzene 18.0 Para-diethylbenzene 80.0 Meta-diethylbenzene 2.0

1000 grams of this feed material is charged to an oxidation vessel and 0.125% cobalt stearate is added thereto. The mixture is stirred and heated under ambient pressure to a temperature of 125 C. A stream of oxygen is bubbled through the reaction mixture while the vessel is maintained at atmospheric pressure. The reaction is continued for 8 hours and then the reaction mixture allowed to cool. The gain of weight after reaction is 11%. Thereafter, the resulting reaction mixture is distilled and various fractions taken.

Fractions: Wt. percent Unreacted diethylbenzene 5.5 Para-ethylacetophene+corresponding carbinol 42.0 Para-diacetylbenzene 33.5 Residue-l-acids 19.0

Acids can be removed either before or after distillation by a caustic washing. Para-diacetylbenzene of analytical purity can be obtained by the removal of minute amounts of ortho and meta-diacetylbenzene by crystallization out of a solvent such as ether. The unreacted diethylbenzene fraction is enriched in ortho-diethylbenzene; in the present example its concentration increases to 34.5%. The ethylacetophenone fraction can be processed as shown in the next example or recycled, together with fresh diethylbenzene, in a next oxidation run.

EXAMPLE VII The reaction system, as in Example VI, is charged with the same hydrocarbon-catalyst mixture. However, oxidation is carried out at 125 C. for only 65 minutes as opposed to the eight-hour period therein employed. Otherwise, oxidation conditions are maintained the same. The gain of weight after reaction is 2.5%. The resulting reaction mixture is distilled and various fractions taken:

Fractions: Wt. percent Unreacted diethylbenzene 53 Ethylacetophenone+corresponding carbinol 35 Diacetylbenzene 6.5 Residue+acids 5.5

Acids can be removed either before or after distillation by a caustic washing. In either case, acids are absent up to the diacetylbenzene fraction. Analysis of the ethylacetophenone fraction is as follows:

Percent Ortho-ethylacetophenone 10.5 Alpha-methyl-ortho-ethyl-benzyl-alcohol 0.5 Meta-ethylacetophenone 1.0

Para-ethylacetophenone 65.0 Alpha-methyl-para-ethyl-benzyl-alcohol 23.0

Carbinols can be removed easily from this mixture by dehydrating them on acid catalysts into ethylstyrenes. It is then quite easy to separate fairly pure orthoand paraethylacetophenone by distillation. For some applications it is not necessary to remove carbinols and then distillation gives on one hand fairly pure ortho-ethylacetophenone and on the other hand a mixture containing essentially para-ethylacetophenone and alpha-methyl-paraethylbenzyl-alcohol. The distillation gap between both isomers is of about 15 C. under 20 mm. Hg allowing an easy separation with an efficient column. It is therefore evident that removing an alphahydrogen atom from a mixture of ortho- +para-diethylbenzene affords an easy separation of both isomers.

Previously meta derivatives of acetophenone were difficult to obtain in a pure form. Starting with pure metadiethylbenzene, several pure meta derivatives can be obtained by controlled oxidation. Some of those derivatives are especially valuable for making heat stable polymers.

Examples 8 and 9 will show how either pure metaethylacetophenone or pure meta-diacetylbenzene can either be obtained in very good yield by choosing proper conditions.

EXAMPLE VIII A feed material is utilized having a composition similar to that of overhead stream 37 of column 29 of Example I. grams of 98% meta-diethylbenzene are charged to an oxidation vessel and 0.15 grams of cobalt stearate are added thereto. The mixture is stirred and heated under ambient pressure to a temperature of C. A stream of oxygen is bubbled through the reaction mixture while the vessel is maintained at atmospheric pressure. The reaction is continued for 90 minutes. The resulting reaction mixture has the following analysis:

Component: Wt. percent Meta-ethylacetophenone 41.53 Meta-diethylbenzene 28.6 Alpha-methyl-meta-ethyl-benzyl-alcohol 10.93 Meta-diacetylbenzene 7.14 Acids-i-residues 7.16

Unknown (including orth- +para-isomers of hereabove volatile products) 4.84

A fraction containing the whole of meta-ethylacetophenone and of alpha-methyl-meta-ethyl-benzyl-alcohol boiling at about 106-107 C./l mm. is easily separated by vacuum distillation. For some applications, i.e., when the ketone is further converted to the carbinol by hydrogenation (intermediate step in the meta-ethyl-styrene synthesis) the ketone and the carbinol do not need to be separated. When the pure ketone is desired the carbinol may either be catalytically dehydrogenated into metaethylacetophenone or catalytically dehydrated into ethylstyrene which is easily removed by distillation. It is thus possible to get meta-ethylacetophenone with a purity of at least 97%. As it will be shown in the next example, a longer reaction time reduces the proportion of carbinol in the ketone but, of course, increases the meta-diacetylbenzene content.

EXAMPLE IX In order to produce mainly meta-diacetylbenzene, an oxidation completely similar to that of Example VIII is carried out except that the reaction is continued for 425 minutes. The resulting reaction mixture has the following analysis:

Component: Wt. percent Meta-diethylbenzene 0.73 Meta-ethylacetophenone 29.9 Alpha-methyl-meta-ethyl-benzyl-alcohol 0.4 Meta-diacetylbenzene 52.1 Acids-l-residues 15.4

Unknown (including ortho- +paraisomers of hereabove volatile products A fraction containing essentially pure meta-diacetylbenzene only contaminated by a small amount of metaethylbenzoic acid and boiling at about 150 to 152 C./ 10 mm. is easily separated by vacuum distillation. The acid can easily be removed by caustic washing and a chemically pure meta-diacetylbenzene melting at 31 to 32 C. is obtained by crystallization out of ether. Any unreacted meta-diethylbenzene and all light oxidation products can be recycled in a next oxidation run. This allows one to obtain a final weight yield of 90 to 100% of metadiacetylbenzene based on meta-diethylbenzene disappearance.

EXAMPLE X A normal ethylbenzene bottoms stream obtained as residue in the preliminary removal of ethylbenzene by distillation had the following analysis:

Component: Wt. percent Ethylbenzene 0.29 C hydrocarbon(ethyl toluene)C (butyl benzene) 2.95 Meta-diethylbenzene 55.23 Para-diethylbenzene 25.40 ortho-diethylbenzene 7.87 Heavy hydrocarbon 8.26

A total of 27 volumes of this stream were fed to a superstill having 239 distillation stages disposed as a series of three columns and operated first at total reflux to produce an equilibrium condition, and then distillation was allowed to proceed at a reflux ratio of 65:1. The overhead was collected as a series of equal volume part fractions, except that the first four volumes of light materials were discarded.

The following table shows the specific analysis of each volume collected as individual samples:

TABLE II Sample Butyl No. MDEB PDEB ODEB E.B benzene Volumes (First 4 volumes discarded) 1 54. 69 4. 99 2. 42 37. 90 1 2 61. 18 15 0.87 17.80 13. 82 1 3 0. 86 30. 45 1 4 l 5 1 6 l 7. 0. 44 0.32 3. 31 0. 46 1 8 1.06 0.76 0.65 1.04 1 9 0. 43 0. 36 0. 46 0. 77 1 10- 0. 38 0. 19 0. 31 0. 53 1 11 0. 28 0. 14 0. 22 0. 35 1 12. 0.87 0.61 0. 74 0. 46 1 13. 0. 44 0. 42 0. 89 0. 66 1 13-11. 1. 49 0. 82 0. 61 0. 65 1 14 0. 94 0. 73 0. 43 0. 54 1 15 0. 74 0. 54 0. 29 0. 37 1 16 1. 57 0. 91 0. 24 0. 32 1 17 3. 25 1. 77 0. 0. 1 18. 7. 28 4. 05 0.11 0. 12 1 19 10. 5. 50 0. 07 0. 07 l 20 84. 14 10. 16 5. 58 0. 06 0. 06 1 21 80. 27 12. 01 7. 0. 07 0. 05 1 22 1 68. 37 20. O6 11. 49 0. 05 0. 03 1 23 52. 04 31. 55 16. 32 0.04 0.05 1

Referring to FIG. 2, as described in detail in Example I, the superfractionator 25 splits a diethylbenzene isomer feed mixture into a meta-rich overhead 37 and a para, orthodiethylbenzene rich bottoms mixture 41. The meta-rich overhead stream 37 is conducted from the refiux condenser 35 to the oxidation reactor 51. Cooling is provided for the oxidation reactor 51 by means of passing water through a water reactor jacket. The product from the oxidation reactor is conveyed to a vessel 53, which is provided with heat transfer means to cool the reaction mixture well below the melting point of isophthalic acid, which precipitates. The resulting slurry is then conveyed to a filter 55, from which isophthalic acid, identified as a product stream 57, is then removed as a solid component. The mother liquor 59 may be utilized for various subsequent processing, recycle in part, or discarded, as desired.

Further referring to FIG. 2, the product stream 41 from column 27 may be conveyed via conduit means 61 to an oxidation reactor 73, which is of the same general nature as the oxidation reactor 51, previously discussed, and the effiuent therefrom conducted to a vessel 65 to obtain solid precipitate high in terephthalic acid content. This precipitate is conveyed, along with the mother liquor from vessel 65 to a filtration unit 67. The mother liquor from the filtration unit, identified as stream 69, may be uilized in various subsequent processing, recycled in part, or discarded as desired. The solid precipitate is transferred from the filtration unit 67 to a wash vessel 71 wherein it is thoroughly washed with cold water, and thereafter conveyed to leaching vessel 73, where hot water, (e.g. 98- 100 C.) thoroughly contacts the precipitate to leach impurities, more particularly phthalic acid, from it. The resulting solid material, identified on FIG. 2 at the arrowhead 75 emerging from vessel 73, is a highly pure terephthalic acid product.

As an alternative to the above, or if desired, as additional means for the process equipment provided for processing diethylbenzenes, the bottoms mixture from the column 27 is conveyed via conduit means 81 to dehydrogenation reactor 83. The efiluent from the reactor is conveyed to a separator 85, wherein water is withdrawn and reaction gases formed in the reaction exit overhead. The hydrocarbon efiiuent 87 from separator is piped to distillation column 89. The overhead product 91 may be utilized for various processing; recycled to the dehydrogenation reactor, at least in part; or disposed of, as desired. The bot- 1 l toms product 93 is transferred through either of two alternate lines 95 or 97 for subsequent processing. If desired, the bottoms stream 93 may be split with part conveyed through the conduit 95 and part through the conduit 97.

Attention is directed first to the process route via conduit '95, by which bottoms product stream 93 enters hydrogenation reactor 98 from line 95. Therein the stream 93 is comparatively mildy hydrogenated. The effluent from hydrogenation reactor 98 is conducted to condenser 99, from which non-condensible gases are removed. The product stream 101 from condenser 99* is piped as a feed to distillation column 103, from which is withdrawn an overhead light fraction 105. The bottoms product 107 from column 103 is piped to column 109 which separates it into an overhead fraction 111 and a bottoms fraction 113. The overhead fraction 111 is paradiethylbenzene product of rather high purity.

The processing of bottoms stream 93 from fractionator 89 will now be described. Bottoms material 93 is conveyed via conduit '97 as feed for column 121, which divides it into an overhead fraction 123 and a bottoms fraction 125. The bottoms fraction 125 may be utilized or discarded as is expeditious. The overhead fraction 123 is conveyed to a crystallizer 126, preferably providing two effective crystallization stages, and a solid product is recovered therefrom, identified by the arrowhead 127 leading from crystallizer 126 of FIG. 2. The solid product 127 is found to be a paradivinylbenzene product of quite high purity. The mother liquor stream 129 is conveyed from the crystallizer and recycled in part, further processed to produce various desired products, or otherwise disposed of.

As an alternate, or in addition, to the oxidation reaction carried out on the para, ortho-diethylbenzene mixture 41 of FIG. 2, other oxidation routes may be provided. Referring to FIG. 3, bottoms material 41 may be conveyed to the oxidation reactor 131, which is suitably cooled. This reactor operates under milder conditions than reactor 63 of FIG. 2, being controlled to produce a substantial quantity of diacetylbenzene product. The effiuent 133 from oxidation reactor 131 is conveyed to distillation column 135, from which exists an undesired overhead fraction 137, and a desired bottoms fraction 139. The bottoms fraction 139 is conveyed to distillation column 141. Column 141 splits the material processed therein into an undesired bottoms 143 and a desired overhead 145, which is conveyed to a crystallizer 147, preferably of two or more stages. If ethylbenzoic acids are to be recovered separately, overhead 145 may first pass through caustic washer 153; caustic washer 153 separates a small amount of para+ortho-ethylbenzoic acids under the form of aqueous salts being indicated on FIG. 3 as the arrowhead 155. If those acids are not to be recovered separately, caustic washer 153 may be omitted. Acids will then stay in mother liquor 151 of crystallizer 147 together with orthodiacetylbenzene and other impurities. A para-diacetylbenzene product of high purity in excess of 97% is obtained as product from crystallizer 147, being indicated on FIG. 3 as the arrowhead 149 emerging from crystallizer 147, Mother liquor 151 is removed from crystallizer 147.

As an alternative method of processing the para, orthodiethylbenzene mixture 41, or processing a part thereof, the mixture 41 is conveyed through oxidizer 161 to obtain efi luent 163 which feeds distillation column 165 from which is withdrawn light fraction 167 as overhead product. Bottoms product from column 165 is conveyed to column 171, which divides it into an undesired bottoms material 173, which is withdrawn and an overhead fraction 175 is conveyed to distillation column 177 providing ample theoretical stages to obtain as overhead substantially pure orthoethylacetophenone being indicated in FIG. 3 as the arrowhead 181 emerging from column 177 and as bottoms fraction, substantially pure para-ethylacetophenone being indicated as the arrowhead 179. Milder oxidation conditions are maintained for the reactor 161, as compared to reactor 131. Consequently, the formation of monoacetyl product as opposed to diacetyl product is favored.

As an alternate, or in addition, to the oxidation reaction carried out on the substantially pure meta-diethylbenzene 37 of FIG. 2, other oxidation routes may be provided. Referring to FIG. 4, overhead meta-diethylbenzene 37 may be conveyed to the oxidation reactor 200 which is suitably cooled. This reactor operates under milder conditions than reactor 51 of FIG. 2, being controlled to produce a substantial quantity of meta-diacetylbenzene product. The eflluent 201 of oxidation reactor 200 is conveyed to distillation column 202 from which exits an undesired overhead fraction 203 and a desired bottoms fraction 204. The bottoms fraction 204 is conveyed to distillation column 205. Column 205 splits the material processed therein into an undesired bottoms 206 and a desired overhead 207 which is conveyed to caustic washer 208. Caustic washer 208 separates a small amount of meta-ethylbenzoic acid in the form of an aqueous salt being indicated on FIG. 4 as the arrowhead 210.

Substantially pure meta-diacetylbenzene 209 may still be optionally purified by crystallizer 211 to a chemically pure product, being indicated as arrowhead 213. Mother liquor 215 is removed from crystallizer 211.

As an alternative method of processing the meta-diethylbenzene 37, or processing a part thereof, the substantially pure meta-diethylbenzene 37 is conveyed through oxidizer 220 to obtain efiluent 221 which feeds distillation column 222 from which is withdrawn light fraction 223 as overhead product. Bottoms product from column 222 is conveyed to column 225 which divides it into an undesired bottoms material 226, which is withdrawn and an overhead fraction 227. This fraction is a mixture of pure meta-ethylacetophenone and of a minor amount of pure alpha-methyl-meta-ethylbenzyl alcohol. For some applications this fraction 227 may be used as such. Optionally, fraction 227 may be fed to dehydrator 228 which splits water from the alcohol; the resulting mixture 239 is passed through the water separator 230 from which water is withdrawn as being indicated by arrowhead 231.

The dehydrated mixture 232 is conveyed to column 233 from which emerges as the overhead product 234 substantially pure meta-ethyl styrene and, as desired, bottoms 238 nearly pure meta-ethylacetophenone. Milder oxidation conditions are maintained for the reactor 220 as compared to reactor 200. Consequently, the formation of meta-ethylacetophenone as opposed to meta-diacetylbenzene is favored.

Thus, applicant performs in certain alternate steps a unique separation of ethylbenzene isomers at least in the first step to separate a substantially pure meta-diethylbenzene overhead from a relatively pure orthoand metadiethylbenzene bottoms fraction. By performing additional or alternate oxidation steps, further purification is available in the form of selected oxidation or dehydrogenation products wherein at least one alpha-carbon atom is oxidized or dehydrogenated into an easily separable derivative to produce such pure products from both the overhead and bottoms fractions. From the overhead pure meta-diacetylbenzene, meta-ethylacetophenone, isophthalic acid, alpha-methyl-meta-ethylbenzyl alcohol or their hydrocarbon analogs, pure diethylbenzene as stated or ethylstyrene, each as a substatnially pure meta-isomer. From the bottoms mixture of predominantly orthoand para-diethylbenzene, we prepare para-ethylacetophenone, para-diacetylbenzene, alpha-methyl-para-ethylbenzyl alcohol, para-divinylbenzene, para-ethylvinyl benzene and the parent hydrogenated isomer para-diethylbenzene.

Other modifications following the principles of this invention are available to produce the same product or other intermediates. For instance, oxidation can be accomplished in two steps one to conversion to a monoacetyl and a subsequent step to convert the mono-acetyl ethylbenzene to diacetylbenzene.

A further advantage of separating in two steps is that intermediate purification may be applied with consequent reduction of reaction products and with ultimate higher purity of the end product.

Thus, the process hereof in addition to preliminary distillation to separate the meta-diethylbenzene includes, as preferred embodiments, oxidation of both overhead and bottoms products to various oxidation products in pure form and to dehydrogenation of the bottoms product followed by rehydrogenation or crystallization to produce a pure para-diethylbenzene in the hydrogenation and a pure para-divinylbenzene in the crystallization. These several purifications, it will be appreciated, are made from a bottom product initially a mixture of orthoand paradiethylbenzene isomers which have been substantially freed of the meta-isomer to a content of less than and usually not more than about 2%.

Ar cordingly, it is intended that the description and examples given hereinabove be regarded as illustrative and not limiting except as defined in the appended claims.

We claim:

1. The process of separating an isometric mixture of diethylbenzenes containing from about 20 to 80% of metaisomer comprising distilling said mixture in a column exceeding about 100 distillation stages to separate an overhead fraction of at least 93% pure meta-diethylbenzene isomers and a bottoms fraction comprising a mixture of orthoand para-diethylbenzene isomers containing less than about 5% of meta-diethylbenzene as contaminant, and oxidizing said bottoms fraction in the liquid phase with a member of the group consisting of oxygen and nitric acid to convert at least one of the ethyl radicals to an oxidized form and thereafter separating the oxidized ortho-diethylbenzene product from the para-diethylbenzene product.

2. The method of separating a meta-diethylbenzene fraction having a purity ranging from at least about 93% to about 99% from a synthetic ethylbenzene formed by alkylation of benzene containing mixed diethylbenzene isomers as impurity, comprising first distilling overhead the ethylbenzene While taking off a side stream comprising some ethylbenzene and C hydrocarbon impurities and leaving a bottoms mixture of isomeric diethylbenzene containing 20 to 80% of meta-diethylbenzene, and the remainder comprising para-diethylbenzene, ortho-diethylbenzene and heavier components, and fractionally superdistilling said diethylbenzene containing bottoms mixture to separate overhead a fraction of meta-diethylbenzene having a purity ranging from at least about 93% to about 99% and paraand ortho-diethylbenzene concen trate bottoms mixture containing less than 2% of metadiethylbenzene in a distillation column exceeding about 100 distillation stages and at a refi'ux ratio exceeding 40:1, oxidizing said bottoms fraction in the liquid phase with a member of the group consisting of oxygen and nitric acid to convert at least one of the ethyl radicals to an oxidized form and thereafter separating the oxidized ortho-diethylbenzene product from the para-diethylbenzene product.

3. 'In the processing of mixed diethylbenzene isomers, the steps of superdistilling a feed comprising mixed meta-,

paraand ortho-isomers of diethylbenzene in a column exceeding about distillation stages and at reflux ratio exceeding 40:1 to obtain a meta-enriched overhead comprising meta-diethylbenzene having a purity ranging from about 93% to about 99% and a low meta-isomer content bottoms mixture, said feed containing meta-diethylbenzene isomer in weight fraction of at least about one-fifth and no greater than about four-fifths, based on the total weight of the meta-, orthoand para-diethylbenzene isomers in said feed, said low meta-isomer content bottoms mixture containing no more than about 5% meta-diethylbenzene based on the total weight of the para-, orthoand metaisomers of diethylbenzene in said low meta-isomer content bottoms mixture, and oxidizing said low meta-content bottoms mixture in the liquid phase with a member of the group consisting of oxygen and nitric acid and thereafter separating the oxidized ortho-diethylbenzene product from the para-diethylbenzene product.

4. The method as defined in claim 3 wherein the said bottoms oxidation product contains para-ethylacetophenone prepared by oxidizing said isomeric bottoms mixture of paraand ortho-diethylbenzene with oxygen, and separating and purifying the para-ethyl-acetophenone from the oxidation.

5. The method as defined in claim 3 wherein the said bottoms oxidation product contains alpha-methyl-paraethyl-benzyl alcohol and ortho-ethyl-acetophenone prepared by oxidizing said isomeric bottoms mixture of paraand ortho-diethylbenzene with oxygen, and separating and purifying the oxidation products.

6. The method as defined in claim 3 wherein the said bottoms oxidation product contains ortho-ethyl-acetophenone prepared by oxidizing said isomeric bottoms mix ture of paraand ortho-diethylbenzene with oxygen, and separating and purifying the ortho-ethyl-acetophenone from the oxidation mixture.

7. The method as defined in claim 3 wherein the said bottoms oxidation product contains para-diacetylbenzene prepared by oxidizing said isomeric bottoms mixture of paraand ortho-diethylbenzene with oxygen, and separating and purifying the para-diacetylbenzene from the oxidation mixture.

8. The method as defined in claim 3 wherein the said bottoms oxidation product contains terephthalic acid pre-- pared by oxidizing said isomeric bottoms mixture of orthoand para-diethylbenzene with nitric acid, and separating and purifying said terephthalic acid from the oxidation mixture.

References Cited UNITED STATES PATENTS 2,959,626 11/1960 Krausse et a1. 260674 2,734,914 2/1956 McKinnis 260-524 XR 3,029,278 4/ 1962 Spiller 260524 BERNARD HELFIN, Primary Examiner US. Cl. X.R. 

